Flexible mold and method of manufacturing microstructure using same

ABSTRACT

To provide a flexible mold capable of easily and correctly manufacturing protuberances such as PDP ribs at predetermined positions with high dimensional accuracy. A flexible mold comprises a support made of a material having a tensile strength of at least 5 kg/mm2 and containing a moisture to saturation at a temperature and a relative humidity at the time of use by moisture absorption treatment applied in advance, and a molding layer having a groove pattern having a predetermined shape and a predetermined size on its surface.

FIELD OF THE INVENTION

This invention relates to a molding technology. More particularly, thisinvention relates to a flexible mold and to a manufacturing method of amicrostructure using the flexible mold.

BACKGROUND

Display devices that use a cathode ray tube (CRT) have economically beenmass-produced owing to the progress and development of televisiontechnologies achieved up to this date, as is well known in the art. Inrecent years, however, a thin and lightweight flat panel display hasdrawn increasing attention as a display device that may replace CRTdisplay devices.

A typical example of such flat panel displays is a liquid crystaldisplay (LCD). LCDs have already been used as compact display devices innotebook type personal computers, cellular telephone sets, personaldigital assistants (PDA), and other mobile electronic informationdevices. Plasma display panels (PDPs) are another example of thin,large-scale flat panel displays. PDPs have been used as wall-hungtelevision receivers for business or home.

For example, FIG. 1 illustrates one example of a PDP 50. In the exampleshown in the drawing, only one discharge display cell 56 is shown in thePDP for simplification, but the PDP includes a large number of smalldischarge display cells. In detail, each discharge display cell 56 isencompassed and defined with a pair of glass substrates opposing eachother in a spaced-apart relation, that is, a front glass substrate 61and a back glass substrate 51, and a rib 54 of a microstructure having apredetermined shape and interposed in a predetermined shape betweenthese glass substrates. The front glass substrate 61 has transparentdisplay electrodes 63 each constituted by a scanning electrode and aholding electrode, and a transparent dielectric layer 62 and atransparent protective layer 64 that are arranged on the substrate 61.The back glass substrate 51 includes address electrodes 53 and adielectric layer 52 formed thereon. The display electrodes 63 consistingof the scanning electrode and the holding electrode, and the addresselectrodes 53 cross one another and are respectively arranged in apredetermined pattern with gaps among them. Each discharge display cell56 has a phosphor layer 55 on its inner wall, and a rare gas (forexample, Ne—Xe gas) is filled into each discharge display cell so thatself-light emission can be effected by plasma discharge between theelectrodes.

A rib (e.g., rib 54 of FIG. 1), which is generally formed of a ceramicmicrostructure, is located on the back glass substrate and constitutes apart of the PDP back plate. As described, in particular, inInternational Patent Publication No. 00/39829 and Japanese UnexaminedPatent Publication (Kokai) Nos. 2001-191345 and 8-273538, a curableceramic paste and a flexible resin mold can be used to manufacture sucha PDP back plate. This flexible mold has a molding layer having grooveportions of a predetermined pattern on a support, and the curableceramic paste can be easily filled into the groove portions due to itsflexibility without entrapping air bubbles. When this flexible mold isused, the mold release operation after curing of the paste can beconducted without damaging the ceramic microstructure (e.g., the rib)and the glass substrates.

To manufacture the PDP back plate, it has been further required toarrange the ribs at predetermined positions with hardly any error fromthe address electrodes. For, if each rib is more correctly disposed atthe predetermined position and its dimensional accuracy is higher,better self-light emission becomes possible.

When the flexible mold described above is used to manufacture the PDPback plate, it is desirable to arrange easily, correctly and with highdimensional accuracy, the ribs at the predetermined positions withoutcalling for a high level of skill. For, when the flexible mold is usedto form the ribs, the ribs can be formed without entrapping the bubblesand without damaging the ribs as described herein.

SUMMARY OF THE INVENTION

The present invention provides a flexible mold that includes a supportand a molding layer. The flexible mold may be used to manufacture PDPribs or other microstructures. Further, the flexible mold may be used toprecisely arrange a protuberance such as a rib at a predeterminedposition with high dimensional accuracy and without defects such asbubbles or pattern deformation.

Typical problems that may occur in the conventional flexible moldsdescribed herein are greatly associated with a use environment of a sizeof a support constituting the mold, that is, fluctuation depending on atemperature and a relative humidity at the time of use of the mold, andconsequently, the problems the solution of which has been believedimpossible in the past can be solved if the mold can keep a desiredpredetermined dimension for at least a predetermined period in its useenvironment.

According to one aspect of the invention, therefore, there is provided aflexible mold including a support made of a material having a tensilestrength of at least 5 kg/mm² and containing moisture to saturation at atemperature and a relative humidity at the time of use by a moistureabsorption treatment applied in advance, and a molding layer disposed onthe support, a surface thereof being provided with a groove patternhaving a predetermined shape and a predetermined size.

According to another aspect of the invention, there is provided a methodof manufacturing a microstructure having a projection pattern having apredetermined shape and a predetermined size on a surface of asubstrate, including preparing a flexible mold including a support madeof a material having a tensile strength of at least 5 kg/mm² andcontaining moisture to saturation at a temperature and a relativehumidity at the time of use by a moisture absorption treatment appliedin advance, and a molding layer disposed on the support, and having agroove pattern having a shape and a size corresponding to those of theprojection pattern on a surface thereof; arranging a curable moldingmaterial between the substrate and the molding layer of the mold andfilling the molding material into the groove pattern of the mold; curingthe molding material and forming a microstructure having the substrateand the projection pattern integrally bonded to the substrate; andreleasing the microstructure from the mold.

As described herein, it may be effective to use a support made of amaterial having rigidity against tension and having a moisture contentin substantial saturation by a moisture absorption treatment applied inadvance, that is, a support substantially containing moisture insaturation, for a flexible mold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing an example of PDP according to theprior art to which the invention can also be applied.

FIG. 2 is a sectional view useful for explaining importance ofdimensional accuracy in a flexible mold.

FIG. 3 is a perspective view showing a flexible mold according to anembodiment of the invention.

FIG. 4 is a sectional view taken along a line IV-IV of FIG. 3.

FIG. 5 is a sectional view serially showing a manufacturing method(former half steps) of a flexible mold according to the invention.

FIG. 6 is a sectional view serially showing a manufacturing method(latter half steps) of a flexible mold according to the invention.

FIG. 7 is a sectional view showing distribution of first and secondcurable materials during a manufacturing process of a flexible moldaccording to the invention.

FIG. 8 is a sectional view serially showing a manufacturing method(former half steps) of a PDP back plate according to the invention.

FIG. 9 is a sectional view serially showing a manufacturing method(latter half steps) of the PDP back plate according to the invention.

DETAILED DESCRIPTION

As described herein with reference to FIG. 1, the ribs 54 of the PDP 50are disposed on the back glass substrate 51 and constitute the PDP backplate. In reference to FIG. 2, a distance c from an inside surface ofone rib 54 to an inside surface of another adjacent rib 54 (i.e., cellpitch) is generally within a range of about 150 μm to about 400 μm,though the value varies depending on screen size. Generally, the ribsmust satisfy two requirements: the ribs should be free from defects suchas entrapment of bubbles and deformation, and the ribs should exhibithigh pitch accuracy. As to pitch accuracy, the ribs 54 may be arrangedat predetermined positions during formation with hardly any error fromaddress electrodes. A positional error of only dozens of microns isacceptable. When the positional error exceeds this level, adverseinfluences occur on an emission condition of visible rays andsatisfactory self-emission display becomes more challenging.

The problem of pitch accuracy of the ribs is critical at present as PDPscreen sizes continue to increase.

When the ribs 54 are viewed as a whole, the total pitch (distancebetween the ribs 54 at both ends) R of the ribs 54 (see, e.g., FIG. 2)must generally have dimensional accuracy of not greater than dozens ofppm, though the value varies to a certain extent depending on the sizeof the substrate and the rib shape. Though it is useful to form the ribs54 by use of a flexible mold 10 including a support 1 and a moldinglayer 11, the total pitch (distance between grooves 4 at both ends) M ofthe mold 10 must also have dimensional accuracy of not greater thandozens of ppm in the same way as the ribs 54.

In the case of the conventional flexible mold 10, the support 1 uses arigid plastic film, and the molding layer 11 having the grooves 4 isformed of a photo-curable resin through molding. The plastic film usedas the support is generally prepared by molding a plastic raw materialinto a sheet, and is commercially available as a roll of the sheet. Theplastic film in the roll form contains little or no moisture because themoisture is lost during its production process and is under a dry state.When such a plastic film under the dry state is used to manufacture amold in combination with a master metal mold, moisture absorption of thefilm starts occurring at the state where the plastic film is taken outfrom the roll, and a dimensional change occurs as a result of expansionof the film. This dimensional change occurs immediately after the moldis withdrawn from the master metal mold, and reaches a level of about300 to about 500 ppm. Therefore, when such techniques are employed,dimensional accuracy of not greater than dozens of ppm necessary for thePDP rib-forming mold may not be achieved.

As further described herein, one embodiment of the present invention maysolve the problem of dimensional accuracy by applying a pre-treatment toa plastic film used to form the mold before it is supplied to the metalmaster mold. This pre-treatment may include applying a moistureabsorption treatment to the plastic film before use. A suitable moistureabsorption treatment is applied to the plastic film by spraying water orsteam to the film, or by immersing the film into water or hot water, orby passing the film through a high-temperature high-humidity atmosphere,so that the moisture content of the film substantially reachessaturation. When such a pre-treatment is applied, the plastic film isstabilized to such an extent that it can no longer absorb the moisture.

To control pitch accuracy of the grooves of the flexible mold to dozensof ppm or below, it may be necessary to select plastic film for thesupport that is harder than the molding material (preferably aphoto-curable material such as a photo-curable resin) constituting themolding layer that is associated with the formation of the grooves.Generally, a curing shrinkage ratio of photo-curable resins is severalpercents (%).

Therefore, when a soft plastic film is used for the support, curingshrinkage of the film invites the dimensional change of the supportitself, and pitch accuracy of the grooves cannot be controlled to dozensof ppm or below. When a rigid plastic film is used, dimensional accuracyof the support itself can be maintained even though the photo-curableresin undergoes curing shrinkage, and pitch accuracy of the grooves canbe kept at a high level of accuracy. When the plastic film is rigid,pitch fluctuation, too, can be restricted to a low level when the ribsare formed. Therefore, the rigid plastic film is advantageous in bothmoldability and dimensional accuracy. Examples of rigid plastic filmssuitable for executing the invention are described herein. As usedherein, the terms “rigid” or “hard” means that the support has requiredhardness, is difficult to undergo deformation in a transverse direction,but imparts required flexibility to the mold.

When the plastic film is rigid, pitch accuracy of the mold dependssolely on the dimensional change of the plastic film. To produce in astable way a mold having desired pitch accuracy, therefore, managementmust be made lest the dimension of the film changes before and after theproduction.

Generally, the dimension of a plastic film reversibly changes dependingon the temperature and the relative humidity of the environment. Asdescribed herein, a commercial plastic film roll hardly containsmoisture because the moisture is lost during the production process.Therefore, when the plastic film is taken out from the roll in anordinary environment, the film absorbs moisture from the ambient air andstarts expanding. When a polyethylene terephthalate (PET) film having athickness of 188 μm is taken out from its roll at 22° C. and 55% RH, forexample, its dimension gradually increases due to moisture absorption,and about 6 hours later, the film stabilizes with a dimensional increaseof 310 ppm.

As will be understood from Comparative Example 1herein, when a mold ismanufactured by using a PET film immediately after it is taken out fromthe roll, the mold has a pitch having a desired dimension immediatelyafter manufacture, but the pitch dimension increases to 310 ppm afterthe passage of one day. In other words, when the plastic film is used tomanufacture the mold immediately after the film is unwound from theroll, it may not be possible to obtain a mold having desired pitchaccuracy. As is described in Example 1, when the PET film is exposed tothe same environment (22° C. and 55% RH) as the environment of themanufacture and is used to manufacture the mold in the same way as inComparative Example 1, pitches having a desired dimension can beobtained. The pitch dimension does not change even after passage of oneday but remains substantially the same as the dimension of the metalmaster mold conjointly used. In other words, when the film is allowed tosufficiently absorb the moisture to stabilize its dimension and is thenused to manufacture the mold, dimensional change of the mold aftermanufacture can be suppressed.

It may be preferred to carry out the moisture absorption treatment ofthe plastic film as quickly as possible. Therefore, one embodiment ofthe present invention may include carrying out the moisture absorptiontreatment at a relatively high temperature. The moisture absorption rateof the plastic film becomes higher with an increasing temperature, andthe time required to reach the saturation moisture content can beshortened when the pre-treatment is carried out at a higher temperature.To stabilize the dimension of a 188 μm-thick PET film, for example, thetreatment time of about 6 hours is necessary at 22° C. and 55% RH, butwhen this condition is changed to 45° C. and 55% RH, the dimension canbe stabilized within about 1 hour.

When the moisture absorption treatment is applied to the plastic filmbefore molding according to the invention, it may be preferred to carryout the treatment at a temperature as high as possible as describedherein. To suppress undesired thermal deformation of the plastic film,however, the high temperature applied to this treatment must be lowerthan the glass transition point (Tg) of the respective plastic films.

Therefore, the treatment temperature for the moisture absorptiontreatment is lower than Tg of the plastic film but is preferably as highas possible. The suitable treatment temperature varies with the plasticfilm used. When the PET film is used, for example, the moistureabsorption treatment is preferably carried out at a temperature around60° C. because its Tg is about 70° C. When the moisture absorptiontreatment is carried out at a high temperature in this way, thepre-treatment time can be drastically reduced and productivity can beimproved.

On the other hand, the saturation moisture content of the plastic filmdepends on the relative humidity and is not affected by the temperature.Therefore, the relative humidity in the moisture absorption step ispreferably equal to that of the production process of the plastic film.The most desirable treatment condition in the moisture absorption stepis a temperature somewhat lower than Tg of the plastic film and arelative humidity substantially equal to that of the film productioncondition. When the moisture absorption treatment is applied under sucha treatment condition, a sufficient amount of the moisture that achievesthe relative humidity of the production environment and the equilibriumstate can be imparted to the film within a short time, and dimensionalfluctuation of the mold after the manufacture can be limited to minimum.

In summary, the support in the flexible mold according to the inventionis not particularly limited so long as it is made of a material havingrigidity against tension and its moisture content is in substantialsaturation due to the moisture absorption treatment applied in advance.However, when the rigidity against tension is expressed in terms of thetensile strength, it is generally at least about 5 kg/mm² and preferablyat least about 10 kg/mm². When the tensile strength of the support isbelow 5 kg/mm², handling property drops when the resulting mold isreleased from the master metal mold or the PDP rib is withdrawn from themold, and breakage and tear may occur.

A support suitable in the practice of the invention is a hygroscopicplastic film from the aspects of easiness of the moisture absorptiontreatment and the handling property, and is further a rigid plasticfilm. Examples of preferred plastic films are polyethylene terephthalate(PET), polyethylene naphthalate (PEN), stretched polypropylene,polycarbonate and triacetate, though these examples are in no wayrestrictive. These plastic films may be used either as a single-layeredfilm or as a composite or laminate film of two or more kinds incombination.

The plastic film that can be advantageously used as the support has atensile strength of various levels. For example, the tensile strength is18 kg/mm² for PET, 28 kg/mm² for PEN, 19 kg/mm² for stretchedpolypropylene, 10 kg/mm² for polycarbonate, and 12 kg/mm² fortriacetate.

The plastic films described above have various moisture contents, thoughvarying depending on the material and the environment of use. Forexample, the moisture content (at 22° C.) of PET is 0.17 wt % at 30% RH,0.21 wt % at 40% RH, 0.25 wt % at 50% RH, 0.32 wt % at 60% RH and 0.38wt % at 70% RH. When measured at 20° C. and 50% RH, the moisture contentis 0.3 wt % for PET, 0.4 wt % for PEN, 0.01 wt % for stretchedpolypropylene, 0.2 wt % for polycarbonate and 4.4 wt % for triacetate.It is estimated that the moisture contents of the respective plasticfilms are generally effective within the range of ±50% of the valuesdescribed above.

The plastic films described above or other supports can be used at avariety of thickness depending on the constructions of the mold and thePDP. The thickness is generally within the range of about 0.05 mm toabout 0.5 mm and preferably from about 0.1 mm to 0.4 mm. When thethickness is outside of these ranges, the handling property may drop. Agreater thickness of the support is more advantageous from the aspect ofstrength.

The flexible mold according to the invention includes a molding layerformed on the support in addition to the support. As will be explainedbelow in detail, the molding layer has on its surface a groove patternhaving a predetermined shape and a predetermined size corresponding tothe PDP ribs as the molding object or other protuberances. The moldinglayer preferably has a two-layered structure of a base layer and acoating layer as will be explained herein, though it may be formed intoa single layer. When the use of a photo-curable molding material istaken into consideration, both support and molding layer are preferablytransparent.

Embodiments of the present invention include a flexible mold and amanufacturing method of a microstructure using the flexible mold.Preferred embodiments of these inventions will be explained hereinafterwith reference to the accompanying drawings. As will be obvious to thoseskilled in the art, however, the invention is not particularly limitedto the following embodiments. Incidentally, the same reference numeralwill be used in the drawings to identify the same or correspondingportion.

FIG. 3 is a partial perspective view that typically shows a flexiblemold according to an embodiment of the invention. FIG. 4 is a sectionalview taken along a line IV-IV of FIG. 3.

As shown in these drawings, a flexible mold 10 has a groove patternhaving a predetermined shape and a predetermined size on its surface.The groove pattern is a lattice pattern defined by a plurality of grooveportions 4 that are arranged substantially parallel to one another whilecrossing one another and keeping predetermined gaps among them. Sincethe flexible mold 10 has the groove portions of the lattice patternopening on the surface, it can be advantageously used for forming PDPribs having a lattice projection pattern, for example, though it can benaturally applied to the manufacture of other microstructures. Theflexible mold 10 may include an additional layer, whenever necessary, oran arbitrary treatment may be applied to each layer that constitutes themold.

However, the flexible mold 10 fundamentally includes a support 1 and amolding layer 11 having groove portions 4 thereon as shown in FIG. 4.Incidentally, the molding layer 11 shown in the drawings includes a baselayer 2 and a coating layer 3. The base layer 2 of the molding layer 11is substantially uniformly made of a first curable material having arelatively high viscosity of 3,000 to 100,000 cps when measured at atemperature of 10° C. to 80° C., but does not substantially or does notat all contain bubbles. Generally, such a first curable material doesnot smoothly undergo shrinkage when cured. Therefore, the mold havingthe grooves made of such a first curable material does not easilyundergo deformation but has excellent dimensional stability.

The first curable material is a heat-curable material or a photo-curablematerial. Particularly when the first curable material is thephoto-curable material, the flexible mold can be manufactured within arelatively short time without calling for an elongated heating furnace.A photo-curable material useful for the first curable material mainlycontains an oligomer (curable oligomer) due to easy availability.Particularly when the oligomer is an acrylic oligomer such as a urethaneacrylate oligomer and/or an epoxy acrylate oligomer, the base layer isoptically transparent. Therefore, when this base layer is combined witha transparent coating layer as will be described herein, the flexiblemold can use a photo-curable molding material because rays of light canbe directed to the molding material even through the flexible mold.

The coating layer 3 is disposed on the surface of the base layer 2proximate the base layer 2. In this instance, bubbles are excludedbetween the base layer 2 and the coating layer 3 on the former. Thecoating layer 3 is substantially uniformly formed of a second curablematerial having a relatively low viscosity of not higher than 200 cpswhen measured at 10° C. to 80° C., but does not substantially or doesnot at all contain bubbles. This second curable material preferably haslow tackiness. Because the coating layer 3 has low tackiness, tackinesson the surface of the flexible mold becomes low. Therefore, the handlingproperty can be improved, and adhesion of the forming mold to thesubstrate and the production apparatus can be prevented.

The second curable material may be either the heat-curable material orthe photo-curable material in the same way as the first curablematerial. Unlike the first curable material, however, the photo-curablematerial useful for the second curable material includes a monomer(curable monomer). Particularly when the monomer is an acrylic monomersuch as acrylamide, acrylonitrile, acrylic acid, acrylic acid ester, andso forth, the coating layer becomes optically transparent. Therefore,the flexible mold can use the photo-curable molding material incombination with the transparent base layer as described above.

The support 1 for supporting the molding layer 11 is preferably aplastic film as already explained in detail, and its thickness isgenerally from about 0.05 mm to about 0.5 mm. Preferably, the support isoptically transparent. When the support is optically transparent, therays of light irradiated for curing can transmit through the support.Therefore, the photo-curable first and second curing materials can beused for respectively forming the base layer and the coating layer.Particularly when the support is uniformly formed of the transparentmaterial, the uniform base layer and coating layer can be formed moreeffectively. Typical examples of the transparent support are describedherein.

The flexible mold according to the invention can be manufactured byvarious means. When the photo-curable first and second curable materialsare used, for example, the flexible mold can be advantageouslymanufactured in the sequence shown in FIGS. 5 and 6.

First, a metal master mold 5 having a shape and a size corresponding tothose of a flexible mold as the object of manufacture, a support 1formed of a transparent plastic film (hereinafter called a “supportfilm”) and a laminate roll 23 are prepared as shown in FIG. 5(A). Here,since the flexible mold is used for manufacturing the PDP back plate, inparticular, the metal master mold 5 has partitions 14 having the samepattern and the same shape as those of the ribs of the PDP back plate onits surface. Therefore, the space (recess) 15 defined by adjacentpartitions 14 is the portion that is to become a discharge display cellof PDP. The laminate roll 23 is one technique for pressing the supportfilm 1 to the metal master mold 5, and known and customary laminatetechniques may be used in place of the laminate roll 23, whenevernecessary.

Next, known and customary coating techniques (not shown) such as a knifecoater or a bar coater may be used to apply the photo-curable firstcurable material 2 to one of the surfaces of the support film 1 to apredetermined thickness as shown in FIG. 5(B). The photo-curable secondcurable material 3 is applied to the partition-holding surface of themetal master mold 5 to a predetermined thickness by the same techniques,and is filled into the recess 15 defined in the gap between thepartitions 14. In this invention, the second curable material 3 is easyto fluidize due to its low viscosity. Therefore, even when the metalmaster mold 5 has the partitions 14 having a high aspect ratio, thesecond curable material 3 can be uniformly filled without entrapping thebubbles.

Next, the laminate roll 23 is caused to slide on the metal master mold 5while the first curable material 2 and the second curable material 3keep adhesion with each other in a direction indicated by arrow A inFIG. 5(C). As a result of this laminate treatment, the second curablematerial 3 can be uniformly removed from the substantial portion of therecess 15.

It may be preferred during this laminate treatment to bring both curablematerials into adhesion while the distance from the top (free end) ofthe partitions 14 to the support film 1 is kept sufficiently greaterthan the height of the partitions (for example, at least 1/10 of theheight of the partitions). For, it is possible to effectively excludemost of the second curable material 3 from the space of the partitions14 and to replace it by the first curable material 2 as shown in FIG. 7.As a result, the base layer 2 can be used for forming the groove patternof the mold besides the coating layer 3.

After the laminate treatment is completed, the rays of light (hv) areirradiated to the first and second curable materials 2 and 3 through thesupport film 1 while the support film 1 is laminated on the metal mastermold 5 as shown in FIG. 6(D). When the support film 1 does not containlight scattering elements such as the bubbles but is uniformly formed ofthe transparent material, the rays of light irradiated hardly attenuateand can uniformly reach the first and second curable materials 2 and 3.As a result, the first curable material is efficiently cured to give theuniform base layer 2 that is bonded to the support film 1. The secondcuring material is similarly cured to give the uniform coating layer 3bonded to the base layer 2.

After a series of manufacturing steps described herein, there isobtained a flexible mold including the support film 1, the base layer 2and the coating layer 3 that are integrally bonded to one another.Thereafter, the flexible mold 10 is released from the metal master mold5 while keeping its integrity as shown in FIG. 6(E).

This flexible mold can be manufactured relatively easily irrespective ofits size in accordance with known and customary laminate means andcoating means. Therefore, unlike the conventional manufacturingtechniques that use vacuum equipment such as a vacuum press machine,this invention can easily manufacture a large flexible mold without anylimitation.

Furthermore, the flexible mold according to the invention is useful formanufacturing various microstructures. As disclosed in JapaneseUnexamined Patent Publication (Kokai) No. 2001-191345, for example, themold according to the invention is particularly and extremely useful formolding ribs of DPD having a lattice pattern. When this flexible mold isemployed, it becomes possible to easily manufacture a large screen PDPhaving lattice ribs, in which ultraviolet rays do not easily leak fromdischarge display cells, by merely using a laminate roll in place ofvacuum equipment and/or a complicated process.

Next, a method of manufacturing a PDP substrate having ribs on a flatglass sheet by using the manufacturing equipment shown in FIGS. 1 to 3of Japanese Unexamined Patent Publication (Kokai) No.2001-191345described above will be explained with reference to FIGS. 8 and 9.

First, as shown in FIG. 8(A), a flat glass sheet 31 having electrodes 32arranged in a mutually parallel configuration with predetermined gapsand prepared in advance is arranged on a support table 21. If a stage,not shown, capable of displacement is used, the support table 21supporting the flat glass sheet 31 thereon is put at a predeterminedposition of the stage.

Next, the flexible mold 10 having the groove pattern on its surfaceaccording to one embodiment of the invention is set to a predeterminedposition of the flat glass sheet 31.

The flat glass sheet 31 and the mold 10 are then positioned relative toeach other. In detail, this positioning is made with eye or by use of asensor 29 such as a CCD camera in such a fashion that the grooveportions of the mold 10 and the electrodes of the flat glass sheet 31are parallel as shown in FIG. 8(B). At this time, the groove portions ofthe mold 10 and the spaces between the adjacent electrodes on the flatglass sheet 31 may be brought into conformity by adjusting thetemperature and humidity, whenever necessary. Generally, the mold 10 andthe flat glass sheet 31 undergo extension and contraction in accordancewith the change of the temperature and humidity, and the degrees ofcontraction/extension are different. Therefore, control is so made as tokeep constant the temperature and humidity when positioning between theflat glass sheet 31 and the mold 10 is completed. Such a control methodis particularly effective for the manufacture of a large-area PDPsubstrate.

Subsequently, the laminate roll 23 is set to one of the end portions ofthe mold 10 as shown in FIG. 8(C). One of the end portions of the mold10 is preferably fixed at this time onto the flat glass sheet 31. Inthis way, deviation of positioning between the flat glass sheet 31 andthe mold 10 previously positioned can be prevented.

Next, as shown in FIG. 8(D), the other free end portion of the mold 10is lifted up and moved with a holder 28 above the laminate roll 23 toexpose the flat glass sheet 31. Caution is to be paid at this time notto impart any tension to the mold 10 so as to prevent crease of the mold10 and to keep positioning between the mold 10 and the flat glass sheet31. Other means may also be employed so long as positioning can be kept.A predetermined amount of a rib precursor 33 necessary for forming theribs is supplied onto the flat glass sheet 31. The example shown in thedrawing uses a paste hopper 27 having a nozzle as a rib precursorfeeder.

Here, the term “rib precursor” means an arbitrary molding materialcapable of forming the rib molding as the final object, and does notparticularly limit the materials so long as they can form the ribmolding. The rib precursor may be of a heat-curing type or aphoto-curing type. As will be explained below with reference to FIG.9(F), the photo-curing rib precursor, in particular, can be usedextremely effectively in combination with the transparent flexible molddescribed above. The flexible mold hardly has defects such as bubblesand deformation and can suppress non-uniform scattering of light. Inconsequence, the molding material is uniformly cured and provides a ribhaving constant and excellent quality.

An example of compositions suitable for the rib precursor basicallycontains (1) a ceramic component giving the rib shape, such as aluminumoxide, (2) a glass component filling gaps between the ceramic componentsand imparting compactness to the ribs, such as lead glass or phosphateglass and (3) a binder component for storing, holding and bonding theceramic components, and a curing agent or a polymerization initiator forthe binder component. Preferably, curing of the binder component doesnot rely on heating but uses irradiation of light. In such a case, heatdeformation of the flat glass sheet need not be taken intoconsideration. An oxidation catalyst consisting of oxides, salts orcomplexes of chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co),nickel (Ni), copper (Cu), zinc (Zn), indium (In) or tin (Sn), ruthenium(Ru), rhodium (Rh), palladium (Pd), silver (Ag), iridium (Ir), platinum(Pt), gold (Au) or cerium (Ce) is added to this composition, whenevernecessary, so as to lower a removal temperature of the binder component.

To carry out the manufacturing method shown in the drawings, the ribprecursor 33 is not uniformly supplied to the entire part of the flatglass sheet 31. In other words, the rib precursor 33 may be supplied toonly the flat glass sheet 31 in the proximity of the laminate roll 23 asshown in FIG. 8(D). For, the rib precursor 33 can be uniformly spreadwhen the laminate roll 23 moves on the mold 10 in the subsequent step.However, a viscosity of about 100,000 cps or below, preferably about20,000 cps or below, is preferably imparted to the rib precursor 33 inthis case. When the viscosity of the rib precursor is higher than about100,000 cps, the laminate roll does not sufficiently spread the ribprecursor, so that air is entrapped into the groove portions of the moldand results in the rib defects. As a matter of fact, when the viscosityof the rib precursor is about 100,000 cps or below, the rib precursoruniformly spreads between the flat glass sheet and the mold only whenthe laminate roll is moved once from one of the end portions of the flatglass sheet to the other, and the rib precursor can be uniformly filledinto all the groove portions without entrapping bubbles. However, thesupplying method of the rib precursor is not limited to the methoddescribed above. For example, the rib precursor may be coated to theentire surface of the flat glass sheet, though this method is not shownin the drawings. At this time, the rib precursor for coating has thesame viscosity as the viscosity described above. Particularly when theribs of the lattice pattern are formed, the viscosity is about 20,000cps or below, preferably about 5,000 cps or below.

Next, a rotating motor (not shown) is driven to move the laminate roll23 on the mold 10 at a predetermined speed as indicated by arrow in FIG.9(E). While the laminate roll 23 moves on the mold 10 in this way, thepressure is serially applied to the mold 10 from one of its ends to theother due to the self-weight of the laminate roll 23. Consequently, therib precursor 33 spreads between the flat glass sheet 31 and the mold 10and the molding material is filled into the groove portions of the mold10. In other words, the rib precursor 33 of the groove portions seriallyreplaces air and is filled. The thickness of the precursor at this timecan be adjusted to a range of several microns to dozens of microns whenthe viscosity of the rib precursor or the diameter, weight or movingspeed of the laminate roll is controlled appropriately.

According to the manufacturing method of the invention shown in thedrawings, even when the groove portions of the mold serve as channels ofair and collect air, they can efficiently discharge air outside or tothe periphery of the mold when they receive the pressure describedabove. As a result, the manufacturing method of the invention canprevent residual bubbles even when filling of the rib precursor iscarried out at the atmospheric pressure. In other words, vacuum need notbe applied to fill the rib precursor. Needless to say, the bubbles maybe removed more easily in vacuum.

Subsequently, the rib precursor is cured. When the rib precursor 33spread on the flat glass sheet 31 is of the photo-curing type, the ribprecursor (not shown) is placed with the flat glass sheet 31 and themold 10 into a light irradiation apparatus 26 as shown particularly inFIG. 9(F), and the rays of light such as ultraviolet rays (UV) areirradiated to the rib precursor through the flat glass sheet 31 and/orthe mold 10 to cure the rib precursor. In this way, the molding of therib precursor, that is, the rib itself, can be acquired.

Finally, the resulting ribs as bonded to the flat glass sheet 31, theflat glass sheet 31 and the mold 10 are withdrawn from the lightirradiation apparatus, and the mold 10 is then peeled and removed asshown in FIG. 9(G). Since the mold according to the invention has highhandling property, the mold can be easily peeled and removed withoutbreaking the ribs bonded to the flat glass sheet.

Though the invention has thus been explained with reference to onepreferred embodiment thereof, the invention is not particularly limitedthereto.

The flexible mold is not particularly limited to the form describedabove so long as it can accomplish the objects and the operation andeffect of the invention. For example, the flexible mold may have aso-called “straight groove pattern” formed by arranging a plurality ofgroove portions in substantially parallel with one another with gapsamong them without crossing one another. Such a flexible mold can beused for forming a rib of PDP of a straight pattern.

The flexible mold according to the invention is not solely used forforming the PDP ribs but can be advantageously used for forming avariety of microstructures having similar shapes or patterns.

Further, the invention can advantageously manufacture the PDP previouslyexplained with reference to FIG. 1 and other types of PDP. Because thedetailed construction, dimensions, etc, of PDP are well known in theart, the explanation will be hereby omitted.

EXAMPLES

The invention will be more concretely explained with reference toseveral examples thereof. However, the invention is not limited to thefollowing examples as will be obvious to those skilled in the art.

Example 1

To manufacture a PDP back plate, this example prepares a rectangularmetal master mold having ribs (partitions) of a straight pattern. Theexplanation will be given in further detail. This metal master mold isconstituted by ribs having an isosceles trapezoidal section and arrangedin a predetermined pitch in a longitudinal direction. The spaces(recess) defined by the adjacent ribs correspond to discharge displaycells of PDP. Each rib has a height of 208 μm, a top width of 55 μm anda bottom width of 115 μM. A pitch (distance between the adjacent ribcenters) is 359.990 μm, and the number of ribs is 2,943. A total pitchof the ribs (distance between rib centers at both ends) is(2,943−1)×0.35999=1,059.091 mm.

A first curable material is prepared by mixing 80 wt % of aliphaticurethane acrylate oligomer (a product of Henkel Co., trade name“Photomer 6010”), 20 wt % of 1,6-hexanediol diacrylate (a product ofShin-Nakamura Kagaku K. K) and 1 wt % of2-hydroxy-2-methyl-1-phenyl-propane-1-on (a product of Ciba SpecialtiesChemicals Co., trade name “Darocure 1173”). When the viscosity of thisfirst curable material is measured by a Brookfield viscometer (B typeviscometer), it is 8,500 cps at 22° C.

A PET film having a width of 1,300 mm and a thickness of 188 μm andwound on a roll (a product of Teijin K. K., a trade name “HPE188”) isprepared to use it as a support of a mold. The PET film is taken outfrom the roll under an environment of 22° C. and 55% RH and is as suchleft standing for 6 hours. A moisture content of the PET film is about0.30 wt %.

Subsequently, a mold is manufactured and inspected in the following waywhile the environment of 22° C. and 55% RH is maintained.

The photocurable resin prepared by the preceding step is applied in aline form to the upstream end of a metal master mold preparedseparately. Next, a PET film subjected to the moisture absorptiontreatment as described above is laminated in such a fashion as to coverthe metal master mold. When the PET film is sufficiently pressed by useof a laminate roll, the photo-curable resin is filled into the recessesof the metal master mold.

Under this state, the rays of light having a wavelength of 300 nm to 400nm are irradiated from a florescent lamp, a product of MitsubishiDenki-Oslam Co., to the photo-curable resin for 30 seconds through thePET film. The photo-curable resin is thus cured and gives a moldinglayer. Subsequently, the PET film is peeled from the metal master moldtogether with the molding layer, and there is obtained a flexible moldhaving a large number of groove portions having a shape and a dimensioncorresponding to those of the ribs of the metal master mold.

When the total pitch of the mold is measured time-wise with the pointimmediately after the peel of the mold from the metal master mold as thestarting point, the measurement result can be obtained as tabulated inthe following Table 1.

Comparative Example 1

A flexible mold is manufactured and inspected in the same way as inExample 1 with the exception that the PET film wound on the roll istaken out and is immediately used under the environment of 22° C. and55% RH without applying the moisture absorption treatment to the PETfilm rolled on the roll for the sake of comparison.

When the total pitch of the mold is measured time-wise with the pointimmediately after the peel of the mold from the metal master mold as thestarting point in the same way as in Example 1, the measurement resultcan be obtained as tabulated in the following Table 1. TABLE 1 change oftotal pitch (unit: mm) metal master time Comparative mold or mold passedExample 1 Example 1 metal master — 1059.091 1059.091 mold* mold  10 min.1059.065 1059.084  60 min. 1059.076 1059.199 180 min. 1059.093 1059.289 1 day 1059.086 1059.394metal master mold* . . . total pitch of ribs of mold

As can be understood from the measurement result shown in Table 1, thetotal pitch of the mold of Example 1 exhibits a change of only about 20ppm after the passage of one day immediately after the production. Thischange amount means that an error is at most about 20 ppm to the totalpitch of the mold as the target, and sufficiently satisfies dimensionalaccuracy of within dozens of ppm required for the mold for the PDP ribs.

In contrast, the total pitch of the mold of Comparative Example 1 issubstantially equal to that of Example 1 immediately after theproduction but gradually increases with time, and reaches about 310 ppmafter the passage of one day. In other words, the total pitch of themold after the passage of one day is greater by about 310 ppm than thetotal pitch of the mold as the target, and fails to satisfy dimensionalaccuracy required for the mold for the PDP rib.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing an example of PDP according to theprior art to which the invention can also be applied.

FIG. 2 is a sectional view useful for explaining importance ofdimensional accuracy in a flexible mold.

FIG. 3 is a perspective view showing a flexible mold according to anembodiment of the invention.

FIG. 4 is a sectional view taken along a line IV-IV of FIG. 3.

FIG. 5 is a sectional view serially showing a manufacturing method(former half steps) of a flexible mold according to the invention.

FIG. 6 is a sectional view serially showing a manufacturing method(latter half steps) of a flexible mold according to the invention.

FIG. 7 is a sectional view showing distribution of first and secondcurable materials during a manufacturing process of a flexible moldaccording to the invention.

FIG. 8 is a sectional view serially showing a manufacturing method(former half steps) of a PDP back plate according to the invention.

FIG. 9 is a sectional view serially showing a manufacturing method(latter half steps) of the PDP back plate according to the invention.

1. A flexible mold comprising: a support made of a material having atensile strength of at least 5 kg/mm² and containing moisture tosaturation at a temperature and a relative humidity at the time of useby a moisture absorption treatment applied in advance; and a moldinglayer disposed on said support, a surface thereof being provided with agroove pattern having a predetermined shape and a predetermined size. 2.A flexible mold as defined in claim 1, wherein said support and saidmolding layer are transparent.
 3. A flexible mold as defined in claim 1,wherein said support is a film comprising a hygroscopic plasticmaterial.
 4. A flexible mold as defined in claim 3, wherein saidhygroscopic plastic material is at least one kind of plastic materialselected from the group consisting of polyethylene terephthalate,polyethylene naphthalate, stretched polypropylene, polycarbonate andtriacetate.
 5. A flexible mold as defined in any one of claims 1,wherein said support has a thickness of 0.05 mm to 0.5 mm.
 6. A flexiblemold as defined in any one of claims 1, wherein said molding layercomprises a base layer made of a first curable material having aviscosity of 3,000 cps to 100,000 cps at 10° C. to 80° C. and a coatinglayer made of a second curable material having a viscosity of not higherthan 200 cps at 10° C. to 80° C., the coating layer being applied over asurface of said molding layer.
 7. A flexible mold as defined in claim 6,wherein said first curable material and said second curable material arephoto-curable materials.
 8. A flexible mold as defined in any one ofclaims 1, wherein the groove pattern of said molding layer is a latticepattern constituted by a plurality of groove portions arrangedsubstantially in parallel while crossing one another with predeterminedgaps among them.
 9. A method of manufacturing a microstructure having aprojection pattern having a predetermined shape and a predetermined sizeon a surface of a substrate, comprising the steps of: preparing aflexible mold comprising a support made of a material having a tensilestrength of at least 5 kg/mm² and containing moisture to saturation at atemperature and a relative humidity at the time of use by a humidityabsorption treatment applied in advance, and a molding layer disposed onsaid support and having a groove pattern having a shape and a sizecorresponding to those of said projection pattern on a surface thereof;arranging a curable molding material between said substrate and amolding layer of said mold and filling said molding material into saidgroove pattern of said mold; curing said molding material and forming amicrostructure having said substrate and said projection patternintegrally bonded to said substrate; and releasing said microstructurefrom said mold.
 10. A manufacturing method as defined in claim 9,wherein said molding material is a photo-curable material.
 11. Amanufacturing method as defined in claim 9, wherein said microstructureis a back plate for a plasma display panel.
 12. A manufacturing methodas defined in claim 11, which further comprises independently arranginga set of address electrodes substantially in parallel with each otherwhile keeping a predetermined gap between them on a surface of saidsubstrate.